Method for femur resection alignment approximation in hip replacement procedures

ABSTRACT

Aspects of the present disclosure involve systems, methods, computer program products, and the like, for utilizing a series of images of a patient&#39;s anatomy to determine a cut plane for use during a hip replacement procedure. To determine a cut plane for use during the procedure, the computer program determines a best fit line through the center of the neck of the femur, as well as a best fit line through the femoral shaft. In one particular embodiment, a cut plane through the femur may then be determined as perpendicular to the center line through the neck of the femur. Further, the location of these features in the images may be determined by analyzing the gray scale value of one or more pixels around a selected point on the image. The pixel with the lowest gray scale value may then be assumed to be the edge of the cortical bone in the 2D image.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part and claims priority to U.S.patent application Ser. No. 14/516,298 entitled “METHOD FOR KNEERESECTION ALIGNMENT APPROXIMATION IN KNEE REPLACEMENT PROCEDURES”,naming II whan Park as inventor and filed on Oct. 16, 2014, the entiretyof which is hereby incorporated by reference herein. This applicationalso claims priority under 35 U.S.C. §119(e) to U.S. ProvisionalApplication No. 61/963,041 entitled “IMPROVEMENTS IN HIP ALIGNMENT ANDRESECTIONING”, filed on Nov. 21, 2013, the entirety of which isincorporated by reference in its entirety herein.

TECHNICAL FIELD

Aspects of the present disclosure generally relate to systems andmethods for an accurate determination of relevant dimensions andalignments (lengths, angles, etc.) associated with a procedure forpartial or total replacement of a hip component of a patient. Additionalaspects of the present disclosure generally relate to systems andmethods for identifying a cortical bone edge in a two-dimensional imageof a hip component of a patient.

BACKGROUND

Through over-use, traumatic events and/or debilitating disease, aperson's joint may become damaged to the point that the joint isrepaired. One type of procedure to address damage to a person's joint isan arthroplasty procedure. Arthroplasty is a medical procedure where ajoint of a patient is replaced, remodeled, or realigned. Damage to thejoint may result in a reduction or wearing away of cartilage in thejoint area, which operates to provide frictional, compressive, shear,and tensile cushioning within the joint. As such, reduction in cartilagein a joint causes pain and decreased mobility of the joint. To combatthis joint pain, a patient may undergo the arthroplasty procedure torestore function and use of the damaged joint.

One type of arthroplasty procedure is known as Total Hip Arthroplasty(THA). In general, THA involves replacing the diseased or damagedportion of the hip with metal or plastic components that are shaped toapproximate the replaced portion or shaped to allow movement of thejoint and relieve the joint pain. Thus, a THA procedure may includereplacement of a portion of the proximal end of the femur and/or aportion of the ilium that make up the hip joint. Similar procedures maybe performed on other damaged joints, such as a knee, an ankle, ashoulder, an elbow, and the like. General discussion of arthroplastyprocedures herein are directed specifically to THA-type procedures, butmay be applied to arthroplasty procedures of other types of joints.

In a THA procedure, a damaged portion of the femur is cut off andreplaced with a metal or plastic component that is shaped to mirror orapproximate the replaced portion. The metal or plastic component may beimpacted onto the femur or fixed using a type of surgical cement orother fastening system. Further, a damaged portion of the ilium may alsobe removed and replaced with a metal or plastic component that is shapedto mirror or approximate the replaced portion. The ilium replacementimplant may also be attached to the ilium through impaction onto thebone or fixed using a type of cement. In essence, the portions of thedamaged hip joint are replaced with prosthetic hip components. Ingeneral, the femur implant and the ilium implant are mated to form aprosthetic joint that approximates the shape and operation of thereplaced hip joint.

As mentioned above, a THA procedure often involves the removal andreplacement of portions of the femur and/or ilium of the injured knee.During the removal, the portions of the femur and ilium may be cut,drilled, resurfaced, and the like to create a surface on the bones thatmates with the respective implants. In one particular example, theproximal end of the femur may be completely removed to create generallyflat surfaces to which the implants are mated. Once the mating surfacesfor the implants are created on the receiving bones, the implants maythen be attached to the bones as described above.

Although the broad outline of the THA procedures is described above,there is much to consider when performing the procedure. For example,patients may undergo a preoperative planning phase including one or moreconsultations with a doctor a month or more before the THA is performed.In addition, alignment of the implants in the joint with the rest of thepatient's anatomy is crucial to the longevity of the implant and theimplant's effectiveness in counteracting the pre-THA joint condition. Assuch, systems and methods have been developed to produce customizedarthroplasty cutting jigs that allow a surgeon to quickly and accuratelyperform the necessary resections of the bones that result in asuccessful THA procedure. In particular, cutting jigs may be generallycustomized for the particular patient's joint undergoing the THAprocedure to ensure that the implants align with the patient's anatomypost-procedure. Through the use of such customized cutting jigs, the THAprocedure is both more accurate (ensuring more longevity to theimplants) and quicker (reducing the time required for the surgicalprocedure, thereby reducing the potential for post-surgerycomplications).

In general, cutting guides or cutting jigs used in THA procedures mayattach to one or more bones of the hip and provide a cut line to thesurgeon for use during the THA surgery. In particular, a femur cuttingjig may attach to one or more portions of the proximal end of the femurand include a cut guide or line. A surgeon, during the procedure,inserts a saw device into or through the cut line to resect the proximalend of the femur. In this manner, the end of the femur is resected bythe surgeon during the THA procedure, thereby creating a smooth matingsurface for the implants. As should be appreciated, the location andangle of the cut plane through the respective bone surface indicated bythe cutting jig may determine the overall effectiveness of the THAprocedure. As such, a cutting jig utilized during the procedure shouldbe designed to provide the proper location and orientation of the cutplane on the bones of the affected joint such that treatment of theregion can be performed accurately, safely, and quickly.

Conventional jigs may be complicated to create, suffer frominaccuracies, overly time consuming to generate, overly expensive togenerate, and many other concerns. Thus, while such systems may beuseful, there are numerous opportunities to advance the art. It is withthese and other issues in mind, among others, that various aspects ofthe present disclosure were developed.

SUMMARY

One implementation of the present disclosure may take the form of amethod for determining a cut plane through a human femur for anarthroplasty procedure on a human hip joint. The method includes theoperations of receiving a plurality of two-dimensional (2D) images of apatient's joint subject to the arthroplasty procedure at a computingdevice, providing a sequence of interior images of a neck of a femurfrom the plurality of 2D images of the patient's joint, the interiorimages corresponding to cross-section images of the neck of the femurand spaced apart by a positive distance, and estimating a centercoordinate for each of the sequence of interior images of the neck ofthe femur, the center coordinate corresponding to a coordinate in aglobal coordinate system of the plurality of 2D images of the patient'sjoint. Additionally, the method may include calculating a best fitlinear segment corresponding to at least two of the center coordinatesfor the sequence of interior images of the neck of the femur,calculating a cut plane for use during the arthroplasty procedure on ahuman hip, wherein the cut plane is perpendicular to the best fit linearsegment corresponding to the at least two of the center coordinates forthe sequence of interior images of the neck of the femur, and generatinga cutting jig for the arthroplasty procedure comprising a cut slotcorresponding to the calculated cut plane.

Another implementation of the present disclosure may take the form of asystem for processing a medical scan of a patient in preparation for anarthroplasty procedure on a human hip joint. The system includes anetwork interface configured to receive one or more medical images of apatient's anatomy, a processing device in communication with the networkinterface, and a computer-readable medium in communication with theprocessing device configured to store information and instructions.Further, when the instructions are executed by the processing device,the instructions perform operations. Such operations may includereceiving a plurality of two-dimensional (2D) images of a patient'sjoint subject to the arthroplasty procedure at a computing device,providing a sequence of interior images of a neck of a femur from theplurality of 2D images of the patient's joint, the interior imagescorresponding to cross-section images of the neck of the femur andspaced apart by a positive distance, and estimating a center coordinatefor each of the sequence of interior images of the neck of the femur,the center coordinate corresponding to a coordinate in a globalcoordinate system of the plurality of 2D images of the patient's joint.Additionally, the operations may further include calculating a best fitlinear segment corresponding to at least two of the center coordinatesfor the sequence of interior images of the neck of the femur,calculating a cut plane for use during the arthroplasty procedure on ahuman hip, wherein the cut plane is perpendicular to the best fit linearsegment corresponding to the at least two of the center coordinates forthe sequence of interior images of the neck of the femur, and generatinga cutting jig for the arthroplasty procedure comprising a cut slotcorresponding to the calculated cut plane.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an anterior view of a patient's pelvic region.

FIG. 2 is a close-up anterior view of a patient's right hip joint.

FIG. 3 is a flowchart illustrating a method for locating a cortical boneedge in a two-dimensional (2D) image of a patient's hip.

FIG. 4 is an illustration of one embodiment for obtaining 2D images of ahip of a patient.

FIG. 5 is a screenshot of a magnetic resonance imaging (MRI) image of apatient's hip.

FIG. 6 is a representative screenshot of a close-up view of an MRI imageof a patient's femur with a selected point and a horizontal pixel rangearound the selected point.

FIG. 7 is a chart illustrating gray scale values of the pixels in thepixel range of the MRI image of FIG. 6.

FIG. 8 is a screenshot of the MRI image of the patient's femur with aselected point and a vertical pixel range around the selected point.

FIG. 9 is a screenshot of the MRI image of the patient's femur with aplurality of horizontal pixel ranges extending from a selected point bya set distance value.

FIG. 10 is a flowchart illustrating a method for determining a cut planeof a femur for use during a hip replacement procedure from one or more2D images of the hip.

FIG. 11 is a perspective illustration of an upper (or proximal) portionof a femur of a patient.

FIG. 12 is a perspective illustration of a femur neck, providing a bestfit line that passes through or near the center axis of the femur neck.

FIG. 13 is a flowchart of a method for determining a plurality ofcontact points on the femur of a patient for use in creating a cuttingjig for a cut plane through the femur.

FIGS. 14A-14C are cross-section views of a femoral neck illustrating afirst, second, and third embodiments in determining two or more contactpoints on the femur neck surface.

FIG. 15 is a perspective view of a hip replacement cutting jig for useduring a hip replacement procedure.

FIG. 16 is a block diagram illustrating an example of a computing deviceor computer system which may be used in implementing the embodimentsdisclosed above.

DETAILED DESCRIPTION

Aspects of the present disclosure involve systems, methods, computerprogram products, manufacturing processes and the like, for utilizing aseries of images of a patient's anatomy to determine a cut plane for useduring a hip replacement procedure, which may be used to create a femurcutting jig useful in a partial or total hip replacement. In particular,the present disclosure provides for a method of utilizing one or moretwo-dimensional (2D) images of the patient's joint to undergo anarthroplasty procedure. The method includes receiving the 2D images ofthe joint from an imaging device and determining the location within atleast one of the 2D images of the patient's cortical bone edge.Ultimately, the jig is fit to cortical bone (the hard outer bonesurface) rather than other parts of the knee being replaced, such assoft tissue surrounding the hip and the like. In general, the locationof the cortical bone edge of the patient's hip is determined byanalyzing the gray scale value of one or more pixels around a selectedpoint on the image. In particular, a range of pixels around the selectedpoint provides a range of gray scale values that may be analyzed todetermine the pixel with the lowest gray scale value. This pixel maythen be assumed to be the edge of the cortical bone in the 2D image.

To determine a cut plane for use during a hip replacement procedure, the2D images may be analyzed by a computer program or a user of a computingdevice to determine several landmarks or aspects of the patient'sanatomy. In one particular example, one or more of the landmarks oraspects may be determined through the edge detection of the corticalbone described above. For example, one or more points along a proximalsurface of the proximal femur in one or more images of the femur may befound through the edge detection. With these points identified, thecomputing device may determine a best fit line through the center of theneck of the femur, as well as a best fit line through the femoral shaft.In addition, an azimuthal angle and a polar angle between the femoralshaft line and the center of the neck of the femur line may also bedetermined. In one particular embodiment, a cut plane through the femurmay then be determined as perpendicular to the center line through theneck of the femur. As such, through the methods described herein, areliable and sturdy cut plane for purposes of a femur implant may bedetermined. Further, the procedure to determine the cut plane throughthe femur does not require the generation of a 3D model of the patient'ship so that the THA procedure may occur more quickly and efficientlythan conventional procedures.

To aid in the description below of the customized arthroplasty cuttingjigs and methods for creating said jigs, a brief discussion of the boneanatomy of the human hip is now included. As mentioned above, thepresent disclosure may be applied to any type of joint of a patient.However, for ease of understanding, the discussion herein is limited toparticulars of the human hip as an example of the joint relating to thepresent disclosure procedure and apparatus.

FIG. 1 illustrates an anterior view of a patient's pelvic region, and inparticular, the femur 106-108 and the ilium 110 that comprise thepatient's hip joints. In FIG. 1, a right hip joint 102 is shown thatincludes the patient's right femur 106 and a socket feature in the rightside of the patient's ilium 110. Similarly, a left hip joint 104 isshown that includes the patient's left femur 108 and a socket feature inthe left side of the patient's ilium 110. The patient's spine 112 isalso illustrated in FIG. 1. A close-up view of the patient's right hip102 is illustrated in FIG. 2 and discussed in more detail below.However, the features of the right hip joint 102 discussed below arealso included in the patient's left hip 104.

As shown in FIG. 2, the patient's right hip joint 202 includes portionsof the patient's right femur 206 and a socket feature 204 of thepatient's ilium 210. More particularly, the hip joint 202 includes thehead of the femur 208 resting within the socket 204. Cartilage 212 andother soft tissues may surround the joint 202 to maintain the femoralhead 208 within the socket 204. Extending laterally from the generallyspherical femoral head 208 is the cylindrically-shaped neck of the femur214, ending at a large, irregular, quadrilateral eminence of the femurknown as the greater trochanter 216. One or more of the components ofthe hip joint 202 are discussed below with reference to the method fordetermining a cut plane for use during a THA procedure.

In general, during a THA procedure, portions of the proximal end of thefemur are removed by the surgeon and replaced with respective implantsthat approximate the shape and function of the end of the bone. To aidin resecting portions of the femur, the surgeon may employ a femurcutting jig that provides a cut or resection line for the surgeon to cutalong. The cut plane provided by the cutting jig may be determined basedon one or more landmarks or features of a patient's anatomy illustratedin an image of the patient's joint. Thus, it may be beneficial fordetermining the cut plane for the THA procedure to accurately identifythe cortical bone, or outer shell, of the patient's femur or ilium fromone or more image slices of the patient's hip. One method for locating acortical bone edge in a 2D image of a patient's bone is described in theflowchart of FIG. 3. Although more or fewer operations may be includedin the process of detecting the cortical bone of the femur, theoperations of FIG. 3 provide an example of one such process thatutilizes 2D images of the patient's joint. Further, although describedherein in relation to detecting a cortical bone edge of a patient'sfemur, similar operations may be performed to locate the bone edge of apatient's ilium in the images or any other bone surface of the patientin the images.

Beginning in operation 302, a series of two-dimensional (2D) images ofthe patient's joint on which the arthroplasty procedure is to beperformed may be obtained. The 2D images of the patient's joint may beobtained from an imaging device (such as an X-ray or magnetic resonanceimaging (MRI) machine) from several aspects of the joint. For example,FIG. 4 illustrates one embodiment for obtaining 2D images of a proximalend of a femur 406 of a patient. In particular, the patient's femur 406is scanned in a MRI coil to generate a plurality of 2D hip coil MRIimages (image slices) of the patient's hip. In one embodiment, the 2Dimages 408 of the hip include a plurality of image slices taken along acoronal plane 408 a through the femur, a plurality of image slices takenalong an axial plane 408 b through the femur, and/or a plurality ofimage slices taken along a sagittal plane 408 c through the femur. Inother embodiments, the 2D images may be any combination of coronal,sagittal and/or axial views. In one embodiment, the MRI imaging spacingfor the 2D hip coil images may range from approximately 2 mm toapproximately 6 mm and may vary from aspect to aspect. For example, thecoronal image slices 408 a may be spaced 2 mm apart, while the axialimage slices 408 b may be spaced 6 mm apart.

While the embodiments herein are discussed in the context of the imagingbeing via an MRI machine, in other embodiments the imaging is viacomputed tomography (CT), X-ray, or other medical imaging methods andsystems. Further, although it is discussed herein as a scan of the hip,the 2D images may be obtained for any joint or other area of thepatient's body, such as images of the patient's ankle, knee, shoulder,etc.

Once the 2D images of the joint at issue are obtained, the images may bereceived at or otherwise provided to a computing device for processing.The computing device may receive the images through any form ofelectronic communication with the imaging device. In one particularexample, the 2D images may be obtained by the imaging device (such asthe MRI imaging machine) and transmitted to a website (and associateddata storage) accessible by the computing device. In general, however,the 2D images may be obtained from the imaging machine in any fashionfor further processing by the computing device. One example of such anMRI image of a patient's hip is illustrated in the screenshot of FIG. 5.In particular, the MRI image 500 is a coronal image slice of a patient'ship roughly along a plane through the middle of the hip illustrating thefemur ilium 502 and the femur 504 of the hip joint. Although the MRIimage 500 of FIG. 5 is referred to for the discussion herein, it shouldbe appreciated that any type of coronal, sagittal, or axial image may beutilized.

In operation 304, the computing device may receive a selected referencepoint in at least one of the 2D images. To provide the reference pointin one embodiment, an operator of the computing device may sit at amonitor or other interface of the computing device through which theimages are viewed. Utilizing a software program executed by thecomputing device, the operator may view the 2D images and provide theone or more reference markers on at least one of the 2D images. Theseelectronic markers may correspond to one or more reference points withinthe images for use by the computing device to determine a cortical boneportion of the bone illustrated in the 2D image. The operations toutilize the reference points to determine the bone edge or the corticalbone in the image are described in more detail below.

In another embodiment, a program executed by the computing device mayobtain the 2D images and determine the one or more reference pointswithin the images, with or without the aid of an operator of thecomputing device. For example, the computing device may analyze the 2Dimages and determine a first reference point within the imagecorresponding to near a presumed cortical bone surface of the bones inthe image. In yet another embodiment, one or more of the operations ofthe method of FIG. 3 are performed by the operator, while otheroperations are performed by the computer program. For example, a programexecuted by the computing device may instruct a user of the device tolocate a reference point in a particular area of the image by requestingthe user to indicate the reference point near what the user may presumeto be the cortical bone edge in the image. In another example, theprogram may analyze the 2D image to locate a potential area in the imagethat may include the cortical bone of the image and instruct the user toselect a reference point within the potential area near a perceivedcortical bone feature. As such, any of the operations and methodsdescribed herein may be performed by an operator of the computing deviceor the computing device itself through hardware, software, or acombination of both hardware and software.

FIG. 6 is a screenshot of a close-up view of an MRI image of a patient'sfemur with a selected point 602 and a horizontal pixel range 604 aroundthe selected point. The image 600 illustrates a non-bone region 606 anda bone region 608 of the patient. For example, the image 600 mayrepresent a small portion of the MRI image 500 shown in FIG. 5 of thepatient's hip joint. The image 600 of FIG. 6 illustrates a portion ofthat image that includes a region 606 illustrating portions of thepatient's hip that does not include the image of the femur and a region608 illustrating portions of the patient's hip that includes the imageof femur bone. In one embodiment, the transition from the non-boneregion 606 to the bone region 608 indicates the edge of the patient'sfemur, or the cortical bone of the patient's femur in the image 600.

Also shown in the image 600 of FIG. 6 is the reference point 602. Asmentioned above, the reference point 602 may be indicated in the imageby the user through operation of the computing device. Thus, the usermay analyze the image and select a point on the image at or near thecortical bone of the femur. In another embodiment, the computing devicemay analyze the image and select a point that is at or near the corticalbone feature of the femur in the image. The reference point 602 may belocated in the image 600 in the non-bone region 606 or in the boneregion 608. Regardless of the embodiment utilized, it should beappreciated that it is not required that the reference point be at thecortical bone edge in the image 600. Rather, the reference point may bein any position within the image, as discussed in more detail below.However, it may be preferable for the reference point 602 to be locatedin the image 600 near the cortical bone edge. By placing the referencepoint 602 near the bone edge in the image 600 ensures that the pixelrange 604 captures the bone edge within the pixel range.

Returning to the flowchart of FIG. 3, in operation 306 the computingdevice may establish a range of pixels 604 in the 2D image around thereference point 602. In the embodiment illustrated in FIG. 6, the rangeof pixels 604 includes pixels along the same horizontal axis of thereference point 602. In particular, the computing device associates theselected reference point 602 to a particular pixel of the image,referred to herein as the reference pixel. In the embodiment shown, thepixel range 604 is the pixels of the image on either side of thereference pixel 602 in the same horizontal axis of the image as thereference pixel. For example, the pixel range 604 may include theadjacent ten pixels to the left of the reference pixel and the adjacentten pixels to the right of the reference pixel. That is, the pixel range602 includes a horizontal row of pixels of the image 600 of twenty-onepixels (the reference pixel, ten pixels to the left of the referencepixel, and ten pixels to the right of the reference pixel). Theparticular row of the image of the range of pixels 602 is determinedfrom the selected reference point or reference pixel 602 in the image.

As should be appreciated, the embodiment illustrated in the image 600 isbut one example of the range of pixels 604 utilized by the computingdevice. In another embodiment, the range of pixels may be a verticalrange of pixels that extend up and down the image from the referencepixel 602. An example of a vertical range of pixels is discussed in moredetail below with reference to FIG. 8. In another embodiment, the rangeof pixels 604 may include a combination of pixels within the same rowand same column as the reference pixel 602. In yet another embodiment,the range of pixels 604 may include pixels not in the same row and/orsame column as the reference pixel 602, or a combination of pixels inthe same row and/or the same column as the reference pixel and pixelsnot in the same row and/or same column. Further, the range of pixels 604may not be adjacent to each other within the range such that spacesbetween the pixels of the range may be present. Also, the range ofpixels 604 may include any number of pixels. For example, it is notrequired that the range of pixels 604 illustrated in FIG. 6 include 21pixels. Rather, the range 604 may include any number of pixels in thesame row of the image as the reference pixel 602. As also discussed inmore detail below, the number of pixels in the range of pixels 604 maybe selected to increase the likelihood that the cortical bone edge inthe image is located within the range. In general, the range of pixels604 around the selected reference pixel 602 may include any number ofpixels in any relation to the reference pixel.

With the range of pixels 604 for analysis established, the computingdevice may analyze the gray scale value associated with one or more ofthe pixels in the range of pixels. FIG. 7 is a chart illustrating thegray scale values of the pixels in the pixel range 604 of the MRI image600 of FIG. 6. Although shown in FIG. 7 as a chart of the gray scalevalues of the pixels in the pixel range, it should be appreciated thatsuch a chart may not be created by the computing device. Rather, thecomputing device may simply analyze the gray scale values associatedwith one or more of the pixels in the pixel range 604 and determine thelowest value of gray scale in the range. However, for simplification ofthe discussion herein, reference is made to the chart of FIG. 7.

The chart 700 includes an x-axis of gray scale values of the pixels inthe image and a y-axis of a reference number assigned to the pixels inthe pixel range 604. In the example shown, the pixels of the pixel rangeare assigned a reference number from 110 to 130. The reference numbersassigned to the pixels may be associated with the placement of thepixels within the pixel range 604. For example, pixel number 110 may bethe leftmost pixel in the pixel range and pixel number 130 may be therightmost pixel. The reference number provided to each pixel in thepixel range 604 may correspond to a reference number used by thecomputing device for that particular pixel in the image 600. Thus, pixelnumber 110 may be the 110^(th) pixel in that particular row of the image600. A similar convention may be used for a vertical pixel range suchthat the lowest reference number may be assigned to lowest pixel in thevertical pixel range and the highest reference number may be assigned tohighest pixel in the vertical pixel range. In general, any type ofreference number may be used to index the pixels in the pixel range 604.In one particular example, the pixels in the image are assigned a pixelnumber by the computing device that is universal to the image and thereference number in the chart may be associated or the same as the pixelnumber assigned by the computing device.

As shown in the chart 700, the gray scale values 702 for each of thepixels 704 in the pixel range 604 are graphed. In operation 310 of theflowchart of FIG. 3, the computing device may analyze the gray scalevalues 702 of the pixels 704 in the pixel range to locate the pixel orpixels with the lowest gray scale value. In the graph 700, the lowestgray scale value 706 occurs at or about pixel 124. Once the pixel withthe lowest gray scale value is determined by the computing device, thecomputing device may then associate the location of the pixel with thelowest gray scale value in the range of pixels as the cortical bone edgeof the image in operation 312. In general, the transition in the imagefrom a darker region to a lighter region may indicate the cortical boneedge in the image. Thus, the location of the pixel in the pixel range604 with the lowest gray scale value indicates the cortical bone edge inthe accompanying image.

In another embodiment, the computing device may be configured to notonly identify the pixel with the lowest gray scale value, but may alsoverify that the gray scale values along the pixel range provide a valleyshape to the graph. The valley shape provides a stronger indication thatthe cortical bone edge is located at the lowest point within the valleyas the gray scale values transition from a dark region to a light regionand back to a dark region along the pixel range. Such a valley suggeststhe cortical bone edge in the image resides in the valley portion of thegray scale value chart 700. In particular, as the x coordinate (704)increases in the graph 700, the gray scale intensity of pixels withinthe range of pixels tends to decrease to a lowest number, correspondingto a highest bone density, then increase beyond that point. Further, insome embodiments the computing device may indicate more than one pixelin the range as being associated with the cortical bone edge in theimage. In this embodiment, a group of pixels may be designated asproviding the cortical bone edge such that the computing device mayassume the cortical bone edge in the image resides somewhere within thegroup of pixels. One such group of pixels in which the cortical boneedge lies in shown in chart 700 as pixels 123-125.

As mentioned above, the computing device may analyze the pixels of therange of pixels to determine the pixel with the lowest gray scale value.In one embodiment, the computing device may calculate the lowest grayscale value of the range of pixels where the pixel intensity can beapproximately expressed as:

I(x,y _(m))=p0m+p1m x+p2m x ² +p3m x ³ +p4m x ⁴, (x=n=n0, m0+1, . . . )

where the row index x assumes values x=1, 2, 3, . . . and thecoefficients p0m, p1m, p2m, p3m, and p4m can be found by inversion of a3×3 or 4×4 matrix involving powers of the pixel index numbers, n=n0,n0+1, n0+2, n0+3, n0+4. The 4^(th) degree of polynomial I(x,y_(m)) inthe equation may be less than 4 in appropriate circumstances. Anapproximation for a location of the “center” of the cortical bone can beestimated by a solution x=(x(min;m) (n0≦x(min)≦n0+4) of the equation

dI(x,y _(m))/dx=p1m+2p2m x+3p3m x ²+4p4m x ³=0.

The method for determining the cortical bone edge in the image of thepatient's femur may also be utilized for other types of pixel ranges. Asmentioned above, the pixel range may be a vertical range, or a number ofpixels in the same column as the reference pixel. FIG. 8 is a screenshotof the MRI image 800 of the patient's femur with a selected point 802and a vertical pixel range 804 around the selected point. Similar to thescreenshot discussed above with reference to FIG. 6, the image 800 mayinclude a reference point 802 associated with a reference pixel of theimage. A range of pixels 804 may also be oriented around the referencepixel. However, in this example, the range of pixels 804 forms avertical column of pixels around the reference pixel. The orientation ofthe range of pixels 804 is just one example of the orientation of therange of pixels associated with the reference point.

In one embodiment, the orientation of the range of pixels may be knownby the computing device when requesting the location of the referencepoint from the user of the computing device. For example, the computingdevice may request the user place the reference point in the image neara particular cortical edge of the bone of the image, such as the outeredge of the medial condyle of the femur in the image. Based on thisrequest, the computing device may then create a horizontally-orientedrange of pixels around the selected reference point to capture thecortical bone edge of the femur in the image. Similarly, the computingdevice may request the user place the reference point in the image nearthe most distal point of the femur in the image. Based on this request,the computing device may then create a vertically-oriented range ofpixels around the selected reference point to capture the cortical boneedge of the femur in the image. In this manner, the computing device mayrequest the placement of the reference point near a particular edge ofthe femur in the image and apply a range of pixels accordingly. In yetanother embodiment, the computing device may analyze the image, select aparticular reference point corresponding to a particular edge of thefemur, and apply a particular orientation of a range of pixels aroundthe reference point to attempt to capture the cortical bone edge of thefemur in the image.

In addition, the computing device may also be configured to analyzeseveral ranges of pixels in relation to determining the edge of the bonein an image based on a reference point in the image. For example, FIG. 9is a screenshot of the MRI image of the patient's femur with a pluralityof horizontal pixel ranges extending from a selected point by a setdistance value. The image 900 is similar to the images described abovewith relation to FIG. 6 and FIG. 8. Also similar to the abovedescription, the computing device may receive a reference point 902 froma user of the computer device or from an analysis of the image 900 bythe computing device. A first range of pixels 904 may be created aroundthe reference pixel 902 as described above and analyzed to determine alowest gray scale value within the range of pixels. However, in additionto locating the pixel with the lowest gray scale value in the firstrange of pixels, the computing device may create additional ranges ofpixels to further locate the cortical bone edge in the image.

In particular, the computing device may be configured to createadditional ranges of pixels 906-916 in relation to the first range ofpixels 904. For example, a second range of pixels 906 may be oriented adistance “d” from the first range of pixels in any direction. In theparticular example illustrated in FIG. 9, the second range of pixels 906is set off from the first range of pixels 904 vertically by thedistance. As such, the second range of pixels 906 is oriented in aseparate row of the image 900 from the first range of pixels 904. Uponthe placement of the second range of pixels 906 in the image 900, thecomputing device may analyze the gray scale values of the pixels in thesecond range of pixels to determine the pixel or group of pixels withthe lowest gray scale value. The edge of the cortical bone in the secondrange of pixels 906 may then be associated with the pixel with thelowest gray scale value. A third range of pixels 908 may then be createdand placed in the image the distance d from the second range of pixels906. The pixels of the third range of pixels 908 may be analyzed todetermine the lowest gray scale value and the cortical bone edge withinthe third range of pixels.

In this manner, multiple ranges of pixels 904-916 may be created andanalyzed to detect the edge of the cortical bone in the image 900.Further, the ranges of pixels 904-916 may be offset from each other bythe distance d in any direction. For example, ranges of pixels 906-910are oriented in rows above the reference point 902, while ranges ofpixels 912-916 are oriented in ranges in rows below the reference point,with the distance between each range of pixels being the value d. Also,the placement of the ranges of pixels 904-916 may be in any directionfrom the reference pixel 902. Thus, ranges of pixels 904-916 may behorizontal or vertical from the first range of pixels 904. In addition,the ranges of pixels 904-916 may be in any orientation, such asvertical, horizontal, blocks, diagonal, etc. and may include more orfewer pixels than the first range of pixels 904. Finally, the distancebetween the ranges of pixels 904-916 may be any distance and may varybetween the various ranges of pixels in the image 900. In this manner,the computing device may utilize pixel ranges 904-916 to locate the edgeof the cortical bone in many locations within the image 900.

In one particular embodiment, the placement of the ranges of the pixels904-916 may be adjusted upon the detection of the cortical bone edge inprevious ranges of pixels. For example, upon the analysis of the secondrange of pixels 906 and the third range of pixels 908 in the image 900,the computing device may determine that the cortical bone is moving tothe right within the ranges of pixels as the ranges of pixels are placedcloser to the top of the image. In such a scenario, the computing devicemay begin orienting additional ranges of pixels to the right from theprevious range of pixels. In this manner, the placement of the ranges ofpixels may be adjusted as the cortical bone edge is determined throughthe analysis of previous ranges of pixels. In a similar manner, theorientation of the ranges of pixels may also be adjusted as the edge ofthe cortical bone is determined. In general, any configurable aspect ofthe range of pixels may be adjusted during the method described as moreinformation about the location of the cortical bone edge is determinedwithin the image.

Through the operations described above, a computing device mayautomatically determine or approximate the cortical bone or edge of thefemur of a 2D image of a patient's hip joint. The location of the boneedge may aid a user of the computing device or the computing deviceitself in determining a cut plane for use in a THA procedure of thepatient's hip. For example, from the 2D images of the patient's hip and,in particular, one or more landmarks of the patient's hip identified inthe 2D images, a cut plane through the patient's femur may be determinedfor use during a hip replacement procedure. The one or more landmarksmay coincide with one or more edges of the patient's bone in the images.Thus, determining one or more edges of the patient's bone in the 2Dimages through the method described above may provide the one or morelandmarks within the images to determine the cut plane used during theresection portion of the THA. Because the method described above is moreaccurate and/or quicker than the user manually identifying the edge ofthe bone edge in the images through a computing device interface, theuse of the method may provide a more accurate cut plane for use duringthe hip replacement procedure.

One example of the use of the edge detection of the patient's bone inone or more 2D images of the patient's joint is now described. Inparticular, a cut plane to resect a portion of a femur for use during apartial or total hip replacement procedure is provided. In general, thecut plane is determined from one or more landmarks or other portions ofthe patient's femur. Such landmarks may be identified in one or moreimage slices of the patient's hip joint and applied to the cut planeorientation. In one particular embodiment, the cut plane may be importedinto a customized cutting jig for use during the THA procedure. Ingeneral, during a THA procedure, portions of the proximal end of thefemur (such as that shown in FIG. 2) are removed by the surgeon andreplaced with an implant that approximates the shape and function of theends of the respective bones. To aid in resecting portions of the femur,the surgeon may employ a femur cutting jig that provides a cut orresection line for the surgeon to cut along.

To determine the cut plane, the computing device may receive the 2Dimages or image slices of the joint from an imaging device and create acustomized jig template from the images. Once the template for thecutting jig is created by the computing device utilizing one or more ofthe landmarks on the 2D images, a cutting or milling program isgenerated by the computing device. The cutting or milling program maythen be provided to a milling machine to create the cutting jigcorresponding to the milling program. The cutting jig is thus customizedto the landmarks identified in the series of 2D images of the patient'sjoint. Further, the procedure does not require the generation of athree-dimensional (3D) model of the patient's anatomy to create thecustomized nature of the cutting jig. Rather, by utilizing one or moremating shapes that contact the joint anatomy at particular contactpoints of the joint anatomy corresponding to the identified landmarks inthe 2D images, the customization of the cutting jig is achieved.Further, because the procedure does not require the generation of a 3Dmodel, the customized cutting jigs may be produced more quickly andefficiently than previous customization methods.

FIG. 10 is a flowchart illustrating a method for determining a cut planeof a femur for use during a hip replacement procedure from one or more2D images of the hip. The operations of the method of FIG. 10 may beperformed by a computing device in operation by a user of the computingdevice. In addition, one or more of the operations may be performed bythe computing device utilizing the cortical bone edge detection methoddiscussed above. In general, the method provides an indication of apotential cut plane for use during a hip replacement procedure. Such acut plane may be translated into a cutting jig for use during theprocedure.

Beginning in operation 1002, a series of two-dimensional (2D) images ofthe patient's joint on which the arthroplasty procedure is to beperformed may be obtained. The 2D images of the patient's joint may beobtained from an imaging device (such as an X-ray or magnetic resonanceimaging (MRI) machine) from several aspects of the joint. Once the 2Dimages of the joint at issue are obtained, the images may be enteredinto a computing device for processing. The computing device may receivethe images through any form of electronic communication with the imagingdevice. In one particular example, the 2D images may be obtained by theimaging device (such as the MRI imaging machine) and transmitted to awebsite accessible by the computing device. In general, however, the 2Dimages may be obtained from the imaging machine in any fashion forfurther processing by the computing device.

In operation 1004, the 2D images of the joint are processed to determinea global coordinate system for the images and/or to identify one or morepoints or landmarks associated with the patient's joint for establishingthe cut plane. In general, a global coordinate system of the patient'sjoint in the images corresponds to the natural alignment of the patientprior to damage to the joint. One particular example of the globalcoordinate system is illustrated in FIG. 11. FIG. 11 is perspectiveillustration of an upper (or proximal) portion of a femur of a patient.Portions of the femur 1102 model may be illustrated in the one or moreimage slices of the patient's femur mentioned above. That is, the femur1102 may be a collection of the image slices of the patient's femur suchthat portions of the femur of FIG. 11 correspond to portions of thepatient's femur, as provided in the received 2D images. In particularand as discussed above, femur 1102 includes a femoral shaft 1108 and afemur head 1104. Extending laterally from the generally sphericalfemoral head 1104 is a cylindrically-shaped neck of the femur 1106,ending at a large, irregular, quadrilateral eminence of the femur knownas the greater trochanter 1110. Also illustrated in the Figure are anestimated line through the center of the femur neck 1112 and anestimated line through the center of the femur shaft 1114. As discussedin more detail below, the femoral neck center axis (FNCA) 1112 andfemoral shaft center axis (FSCA) 1114 may be determined by the computingdevice through an analysis of the images of the patient's femur 1102.

Also included in FIG. 11 is a global coordinate axis 1120. In general,the global coordinate system 1120 includes an x-axis, y-axis, and az-axis. In one particular embodiment, the z-axis coincides with, or isapproximately parallel to, a direction of a line segment through thefemoral neck 1106, or the femoral neck center axis 1112. As such, thecomputing device may determine the FNCA 1112 directly from the images,or an approximation of the FNCA may be provided to the computing device,such as from a user of the device. In one specific example, the user mayprovide a center axis reference line in one or more of the images thatapproximates the FNCA 1112. Also, the x-axis and the y-axis of theglobal coordinate system 1120 may be oriented in a plane that istransverse or perpendicular to the z-axis. As should be appreciated, theglobal coordinate system 1120 of FIG. 11 is but one system that may beused in the present disclosure. In general, the global coordinate system1120 may lie in any orientation in relation to the 2D images.

In one particular embodiment, one or more of the 2D images may bereformatted along the global coordinate system 1120. For example, thereformatting of the images may include reorientation of the imagesand/or extrapolation of data from between image slices to align orapproximate the global coordinate system 1120. Thus, each of the 2Dimages in the set of images may be reformatted to account for the angleof the images obtained during imaging. In one embodiment, one or morereference lines or points within the images may be analyzed whenreorienting or reformatting the images along the global coordinatesystem. Such reference points or reference lines may be obtained throughthe operations described above to locate the edge of the femur bone inthe images provided to the computing device. In yet another embodiment,the global coordinate system 1120 may be determined by the computingdevice in relation to the image or images with no additional formattingof the images occurring.

In operation 1006, a computing device estimates the center coordinatesof the femur neck 1106 in two or more of the 2D images that include thepatient's femur 1102. In one particular embodiment, the computing devicemay utilize a sequence of approximately parallel images, spaced apartalong the FNCA 1112 of the femur neck (along the z-axis of the globalcoordinate system 1120). As should be appreciated, however, it is notrequired that the images be along the z-axis, but may be oriented in anymanner in the coordinate system 1120. Also, as described below, thecomputing device may utilize two or more such images when determiningthe center of the femur neck 1106 depicted in the images of thepatient's femur 1102.

Viewed along the z-axis, the selected images form a general oval-shape,representing a cross-section view of the femur neck 1106. For example,FIG. 11 includes two such image slices through the femur neck 1106,cross-section image 1116 and cross-section image 1118. As shown,cross-section image 1116 and cross-section image 1118 are separatedalong the femur neck 1106 (and subsequently along the z-axis of thecoordinate system 1120) by a distance d. In general, distance d betweenthe images may be any distance along the femur neck 1106.

Once the cross-section images 1116, 1118 are selected, the computingdevice may then estimate a center of the ovals in the selected images.For example, FIG. 12 is a perspective illustration of the femur neck1106 of FIG. 11, including image slice 1116 and image slice 1118 throughthe neck. As mentioned, each slice through the femur neck 1106 providesa mostly oval-shape when viewed along the z-axis of the globalcoordinate system 1120. Thus, the computing device may estimate a centerof the oval-shape for each of the image slices 1116, 1118 selected bythe computing device. In particular, image slice 1116 includes estimatedcenter point 1124 and image slice 1118 includes estimated center point1126. Further, the computing device may determine a coordinate in thecoordinate system associated with each estimated center point, such thatcenter point 1124 may correspond to coordinate point (x_(c)(1),y_(c)(1)) and center point 1126 may correspond to coordinate point(x_(c)(2), y_(c)(2)). Further, additional images slices 1122 and centerpoints 1128 (with associated coordinate points ((x_(c)(k), y_(c)(k)) maybe determined by the computing device. In general, any number of imagesslices may be selected by the computing device.

In one particular embodiment, a sequence of two dimensional coordinates(xm(k),ym(k)) (numbered m=1, . . . , M) of spaced apart locations oneach oval (numbered k=1, . . . , K) is measured, and coordinates(x_(c)(k),y_(c)(k)) of geometric center for each oval are estimated as

M

(x _(c)(k),y _(c)(k))=Σ(x _(m)(k),y _(m)(k))/M.

m=1

These points may then be assumed as the estimated centers of theselected image slices along the femur neck 1106 by the computing device.

Once the centers of the image slices 1116, 1118 through the femur neck1106 are estimated, the computing device may determine a best fit linearsegment adjacent to or near the estimated image slice centers inoperation 1008. One best fit linear segment 1130 is shown in FIG. 12 forthe image slices 1116, 1118 through the femur neck 1106. In general, thebest fit linear segment 1130 may be determined by the computing deviceby minimizing an error function that provides a measure of an errorbetween each of the center coordinate locations and the coordinates ofthe best fit linear segment as the segment passes through the associatedimage slice. In this manner, the best fit linear segment 1130 is createdthat passes through or near the center coordinates 1124-1128 of theimage slices along the femur neck 1106. In one embodiment, the best fitlinear segment 1130 may be utilized by the computing device as a femurneck central axis (FNCA) line 1112 through the femur neck 1106. Asdescribed in more detail below, a cut plane used during a hipreplacement procedure may be determined by the computing device as beingperpendicular to the FNCA 1112 line through the femur neck 1106.

In a similar manner in determining the FNCA line 1112 through the neck1106 of the femur, the computing device may determine a best fit linearsegment for the femur shaft 1108 in operation 1010. Thus, in oneembodiment, the computing device may obtain image slices through thefemur shaft 1108, estimate a center of two or more images through thefemur shaft, and calculate a best fit segment line 1114 through or nearthe determined center coordinates of the selected image slices. Thisline through the femur shaft 1108 may be utilized by the computingdevice as the femur shaft central axis (FSCA) line 1114.

In operation 1012, the computing device may then calculate an azimuthalangle φ 1140 and a polar angle ⊖ 1142 of the FNCA 1112 relative to theFSCA 1114. In particular, the two angles (the azimuthal angle φ and apolar angle ⊖) may be estimated or calculated by the computing deviceutilizing two or three transversely oriented views of the femur neck1106 and the femur shaft 1108 relative to each other. In other words, byknowing the orientation of the FSCA 1114 and the FNCA 1112 in the globalcoordinate system 1120, the computing device calculates the azimuthalangle φ 1140 and a polar angle ⊖ 1142 between the two line segments. Theazimuthal angle φ 1140 and a polar angle ⊖ 1142 are illustrated in FIG.11, although it should be appreciated that these angles lie in thethree-dimensional global coordinate system 1120 of the Figure.

As explained above, this calculated information may be used to determinea cut plane through the femur neck 1106 during a THA or other type ofhip replacement procedure. For example, in operation 1014, a cut planemay be determined along the femur neck 1106 that lies perpendicular tothe FNCA line 1112 determined above. In one embodiment, a surgeon maydetermine an appropriate distance from the end of the femur forpositioning of the cut plane along the z-axis of the femur neck 1106based on at least the implant intended for the particular patient. Ingeneral, however, the cut plane is oriented to be perpendicular to theFNCA 1112 determined above. As such, through the operations describedabove, the orientation of a cut plane may be determined from the 2Dimages provided to the computing device. In this manner, variouslandmarks of the patient's femur illustrated in the 2D images of thepatient's hip may be utilized to determine an orientation of a cut planeto be used during a THA procedure. Such a cut plane may be determinedwithout the need to model the patient's hip or otherwise create a 3Dinterpretation of the images.

In addition to determining the orientation of a cut plane through thefemur neck 1106 that is perpendicular to an estimated FNCA 1112, thecalculations above may also be utilized to create a hip alignment andresectioning mechanism, or cutting jig that provides a guide for thedetermined cut plane. Also, such a cutting jig may include one or morecontact points to stabilize the cutting jig on the femur and preventrotation of slippage of the cutting jig from the proper position on thefemur. FIG. 13 is a flowchart of a method for determining a plurality ofcontact points on the femur 1102 of a patient for use in creating acutting jig for a cut plane through the femur. The operations of themethod of FIG. 13 may be performed by the computing device to create amilling program or instructions for creation of a cutting jig to be usedduring a hip replacement procedure.

Beginning in operation 1302, the computing device may estimate thelength of the femur neck illustrated in the 2D images of the femur.Using the femur 1102 of FIG. 11 as an example, the computing device mayestimate the length of the femur neck 1106 from the intersection of thefemur neck with the femur shaft 1108 to the intersection of the femurneck to the femur head 1104. In the particular embodiment shown, imageslice 1116 may represent the intersection of the femur neck 1106 withthe femur shaft 1108 and image slice 1117 may represent the intersectionof the femur neck to the femur head 1104.

In operation 1304, the computing device selects an image slice throughthe femur neck 1106 adjacent or near the intersection of the femur neckwith the femur shaft 1108 (image slice 1116) and estimates a length of afirst minimum diameter for the for the selected image slice. Once thefirst minimum diameter for the selected image slice is determined, thecomputing device identifies a first and second contact point on thefemur neck 1106 located at first and second ends of the first minimumdiameter. For example, FIG. 14A illustrates an example image slicethrough the femur neck 1106. The image slice 1402 may be the selectedimage slice adjacent or near the intersection of the femur neck with thefemur shaft 1108. In one embodiment, the computing device, utilizing theselected image slice 1402, determines the minimum diameter 1404 for theimage slice and identifies a first contact point 1406 and a secondcontact point 1408 on the femur neck located at first and second ends ofthe first minimum diameter.

In operation 1306, the computing device identifies first and secondcontact regions on the femur neck 1106 that include the respective firstand second contact points identified above. In other words, thecomputing device determines a region on the femur neck 1106corresponding to each contact point that also includes each respectivecontact point. These contact regions, as explained in more detail below,may be utilized to determine contact points for a cutting jig for useduring a THA procedure on the femur 1102.

In a similar manner as above, the computing device may identify a thirdand fourth contact point on a second image slice through the femur neck1106 in operation 1308. The second image slice may be adjacent or nearthe intersection of the femur neck with the femur head 1104 (image slice1117). With the selected image slice, the computing device estimates alength of a second minimum diameter for the for the selected secondimage slice and identifies a third and fourth contact point on the femurneck 1106 located at third and fourth ends of the second minimumdiameter. Also similar to above, the computing device may identify athird contact region on the femur neck 1106 that include the determinedthird contact point identified above in operation 1310. This thirdcontact region, as explained in more detail below, may be utilized todetermine a contact point for a cutting jig for use during a THAprocedure on the femur 1102.

In operation 1312, the computing device provides for a hip alignment andresectioning mechanism having at least first, second and third contactextensions that mechanically connects the first and second and thirdcontact point regions so that, with the first, second and third contactextensions connected to the respective first, second and third contactpoint regions, the mechanism will resist movement of any one of thefirst second and third contact extensions relative to the respectivefirst, second, and third contact point regions. One example of such acutting jig is illustrated in FIG. 15. As shown, the cutting jig 1502may include a first contact 1504 on a first contact region of the femurneck 1106, a second contact 1506 on a second region of the femur neck,and a third contact 1508 on a third region of the femur neck. As shouldbe appreciated, however, the cutting jig 1502 illustrated in FIG. 15 isbut one example of the shape and style of a cutting jig. In general, thecutting jig 1502 may be of any shape that includes the three contactpoints as described above. In addition, the cutting jig 1502 may providea cut plane aperture 1512 that permits a selected portion of the femurheard and/or femur neck to be removed in operation 1314. In oneparticular embodiment, the cut plane through the femur neck may beperpendicular to a FNSA through the center of the femur neck, asdescribed above.

In general, the computing device may determine the measurements andcalculations discussed above in any manner. However, provided below areseveral embodiments of the present disclosure for determining one ormore of the contact regions discussed above. In a first embodiment,illustrated in FIG. 14A, (x,y) coordinates for an image are measured andused with an algorithm to estimate a plurality of ellipse lengthparameters, a and b, and an ellipse rotation parameter Ψk that provide aBest Fit Ellipse BFE(k) 1410, as described by equations:

(x′ak)²+(y′/bk)²=1(0<bk≦ak)

x′k=(x−xc(k))cosΨk+(y−yc(k))sinΨk,

y′k=−(x−xc(k))sinΨk+(y−yc(k))cosΨk.

Here, parameters ak and bk are the lengths of the major and minor axesfor the ellipse E(k), respectively, and Ψk is a Best Fit angle ofrotation of the ellipse BFE(k) 1410 relative to the original coordinatesystem axes (x,y). Two contact points, 1406 and 1408, are defined by theellipse minor axis with the ellipse E(k) and provide two spaced apartantipodal locations for attachment of a hip alignment and resectionmechanism, which may be fabricated and used for the femur neck 1106. Thetwo spaced apart antipodal contact points are identified for each of theBest Fit Ellipses, BFE(k=k1) and BFE(k=k2), located adjacent to thefirst end and the second end, respectively, of the femur neck 1106.

The length d12(min) 1404 of a line segment L12 1412 extending betweenthe two contact points, 1406 and 1408, for the ellipse BFE(k) 1410,shown in FIG. 14A is a minimum distance for two antipodal points on theellipse BFE(k). Because this distance is a minimum, rotation of thesetwo contact points on the femur neck surface, lying in a planeperpendicular to the femur neck central axis FNCA 1112, requires anincrease in this separation distance. This increase is resisted ineither direction by a portion of the mechanism that incorporates thesetwo antipodal contact points, 1406 and 1408. A pair ofminimum-separation antipodal contact points are located on the femoralneck surface, adjacent to each of these two pairs, in a plane that isperpendicular to the central axis FNCA 1112, will be resisted by aportion of the mechanism 1502 mechanically connected to these twoantipodal contact points. Longitudinal movement of the mechanismparallel to the FNCA 1112 of the femur neck 1106 is resisted in eitherlongitudinal direction by abutment of a first end of the mechanism 1502against an intersection of the femur neck and the femur shaft, and/or byabutment of a second end of the mechanism against an intersection of thefemur neck and the femur head 1104. Optional provision of an end segmentETL12, oriented approximately parallel to the segment L12 and passingthrough a single point (major axis point) on the ellipse BFE(k) 1410,will provide a third contact point 1414 (and, optionally, a fourthcontact point) for the image 1402, if such end segment is needed. Theend segment ETL12 intersects tangent lines TL1 and TL2, that passthrough the contact points 1406 and 1408, at arbitrary angles φ1 and φ2,where φ1+φ2=π. Optionally, φ1 and φ2 may each be equal to π/2, asindicated in FIG. 14A.

In a second embodiment, illustrated in FIG. 14B, a central point ororigin (xc(k),yc(k)) 1428 is again identified on the image 1426 asdiscussed above and a length is measured for each of a sequence of linesegments that pass through the center (xc(k),yc(k)) and intersect theimage. At least one line segment L34(min) has a minimum length d34(min),and the intersection of the line segment L34(min) with the image definestwo contact points, denoted 1420 and 1422 lying in a plane perpendicularto the FNCA 1112. Note that distances r3 and r4, between the center(xc(k),yc(k)) 1428 and the respective contact points 1420 and 1422 neednot be equal to each other because points 1420 and 1422 lie on theimage, not on a Best Fit Ellipse for the image as in the embodimentabove. The total length d34(min)=r3+r4 is minimized in this embodiment.One advantage of this second embodiment, relative to the firstembodiment, is that the image is used directly, with no construction ofa Best Fit ellipse for the image. Again, a pair of contact points (1420and 1422) is identified for each of a first image and a second image,located at first and second ends of the femur neck 1106, and each pairof these contact points resists rotation on the femur neck surface ineither direction in a plane perpendicular to the FNCA 1112. Lines TL3and TL4 that are tangent to the image at the contact points, 1420 and1422, are not necessarily parallel to each other. Optional provision ofan end segment ETL34, oriented approximately parallel to the segment L34and passing through a single point 1424 on the image, illustrated inFIG. 14B, may provide a third contact point for the image 1426. The endsegment ETL34 intersects tangent lines TL3 and TL4, that pass throughthe contact points 1420 and 1422 at arbitrary angles φ3 and φ4, whereφ3+φ4=constant. Here, this sum of angles φ3 and φ4 need not be equal toit, because the tangent lines TL3 and TL4 need not be parallel.

In a third embodiment, illustrated in FIG. 14C, for each of a sequenceof pairs of parallel lines, TL5 and TL6, that pass through spaced apartpoints on the image and are parallel to each other, a length d56 of aline segment L56 connecting these two points is measured. At least onepair of such points, denoted and lying in a plane perpendicular to theFNCA 1112, 1430 and 1432, is found for which the length, denotedd56(min), is a minimum, and these two points serve as contact points forthe mechanism 1502. The parallel nature of the two tangent lines TL5 andTL6 is enforced by construction of the mechanism. Where an attempt ismade to move the contact point 1430 and/or the contact point 1432, whilepreserving the parallel nature of the two corresponding tangent lines,the distance d56 will increase, and this attempted move will be resistedby the mechanism 1502. Note that the line segment L56 need not passthrough the center (xc(k),yc(k)) 1440 for the image 1438, and thiscenter need not even be identified in this third embodiment. These areadvantages of the third embodiment relative to the second embodiment andrelative to the first embodiment. Optional provision of an end segmentETL56, oriented parallel to the segment L56 and passing through a singlepoint 1434 on the image, will provide a third contact point for theimage. The end segment ETL56 intersects tangent lines TL5 and TL6 thatpass through the contact points 1430 and 1432 at arbitrary angles φ5 andφ6, where φ5+φ6=n, because the tangent lines TL5 and TL6 are parallel.

In each of the first, second and third embodiments, the correspondingthird location, 1410, 1424 or 1434, can serve as a third contact pointfor the corresponding image. Preferably, the length of the mechanism1502 for a particular embodiment is chosen to be approximately equal tothe length of the femur neck 1106, measured from the first end(intersection of the femur shaft 1108 and the femur neck) to the secondend (intersection of the femur head 1104 and the femur neck). Each ofthe first, second and third contact point locations (and, optionally, afourth contact location) in any of the preceding embodiments has acorresponding contact point region, with a small, positive numericalarea associated therewith. The mechanism 1502, illustrated in FIG. 15,comprises three (or optionally four) contact extensions thatmechanically connect to the respective three (or, optionally, four)contact point regions. With the three (or four) contact extensionsconnecting the respective three (or four) contact point regions, themechanism 1502 resists movement on the femur neck 1106 surface of anyone of the contact extensions relative to the corresponding contactpoint region.

FIG. 16 is a block diagram illustrating an example of a computing deviceor computer system 1600 which may be used in implementing theembodiments disclosed above. The computer system (system) includes oneor more processors 1602-1606. Processors 1602-1606 may include one ormore internal levels of cache (not shown) and a bus controller or businterface unit to direct interaction with the processor bus 1612.Processor bus 1612, also known as the host bus or the front side bus,may be used to couple the processors 1602-1606 with the system interface1614. System interface 1614 may be connected to the processor bus 1612to interface other components of the system 1600 with the processor bus1612. For example, system interface 1614 may include a memory controller1618 for interfacing a main memory 1616 with the processor bus 1612. Themain memory 1616 typically includes one or more memory cards and acontrol circuit (not shown). System interface 1614 may also include aninput/output (I/O) interface 1620 to interface one or more I/O bridgesor I/O devices with the processor bus 1612. One or more I/O controllersand/or I/O devices may be connected with the I/O bus 1626, such as I/Ocontroller 1628 and I/O device 1630, as illustrated.

I/O device 1630 may also include an input device (not shown), such as analphanumeric input device, including alphanumeric and other keys forcommunicating information and/or command selections to the processors1602-1606. Another type of user input device includes cursor control,such as a mouse, a trackball, or cursor direction keys for communicatingdirection information and command selections to the processors 1602-1606and for controlling cursor movement on the display device.

System 1600 may include a dynamic storage device, referred to as mainmemory 1616, or a random access memory (RAM) or other computer-readabledevices coupled to the processor bus 1612 for storing information andinstructions to be executed by the processors 1602-1606. Main memory1616 also may be used for storing temporary variables or otherintermediate information during execution of instructions by theprocessors 1602-1606. System 1600 may include a read only memory (ROM)and/or other static storage device coupled to the processor bus 1612 forstoring static information and instructions for the processors1602-1606. The system set forth in FIG. 16 is but one possible exampleof a computer system that may employ or be configured in accordance withaspects of the present disclosure.

According to one embodiment, the above techniques may be performed bycomputer system 1600 in response to processor 1604 executing one or moresequences of one or more instructions contained in main memory 1616.These instructions may be read into main memory 1616 from anothermachine-readable medium, such as a storage device. Execution of thesequences of instructions contained in main memory 1616 may causeprocessors 1602-1606 to perform the process steps described herein. Inalternative embodiments, circuitry may be used in place of or incombination with the software instructions. Thus, embodiments of thepresent disclosure may include both hardware and software components.

A machine readable medium includes any mechanism for storing ortransmitting information in a form (e.g., software, processingapplication) readable by a machine (e.g., a computer). Such media maytake the form of, but is not limited to, non-volatile media and volatilemedia. Non-volatile media includes optical or magnetic disks. Volatilemedia includes dynamic memory, such as main memory 1616. Common forms ofmachine-readable medium may include, but is not limited to, magneticstorage medium; optical storage medium (e.g., CD-ROM); magneto-opticalstorage medium; read only memory (ROM); random access memory (RAM);erasable programmable memory (e.g., EPROM and EEPROM); flash memory; orother types of medium suitable for storing electronic instructions.

It should be noted that the flowcharts above are illustrative only.Alternative embodiments of the present invention may add operations,omit operations, or change the order of operations without affecting thespirit and scope of the present invention. The foregoing merelyillustrates the principles of the invention. Various modifications andalterations to the described embodiments will be apparent to thoseskilled in the art in view of the teachings herein. It will thus beappreciated that those skilled in the art will be able to devisenumerous systems, arrangements and methods which, although notexplicitly shown or described herein, embody the principles of theinvention and are thus within the spirit and scope of the presentinvention. From the above description and drawings, it will beunderstood by those of ordinary skill in the art that the particularembodiments shown and described are for purposes of illustrations onlyand are not intended to limit the scope of the present invention.References to details of particular embodiments are not intended tolimit the scope of the invention.

We claim:
 1. A method for determining a cut plane through a human femur for an arthroplasty procedure on a human hip joint, the method comprising: receiving a plurality of two-dimensional (2D) images of a patient's joint subject to the arthroplasty procedure at a computing device; providing a sequence of interior images of a neck of a femur from the plurality of 2D images of the patient's joint, the interior images corresponding to cross-section images of the neck of the femur and spaced apart by a positive distance; estimating a center coordinate for each of the sequence of interior images of the neck of the femur, the center coordinate corresponding to a coordinate in a global coordinate system of the plurality of 2D images of the patient's joint; calculating a best fit linear segment corresponding to at least two of the center coordinates for the sequence of interior images of the neck of the femur; calculating a cut plane for use during the arthroplasty procedure on a human hip, wherein the cut plane is perpendicular to the best fit linear segment corresponding to the at least two of the center coordinates for the sequence of interior images of the neck of the femur; and generating a cutting jig for the arthroplasty procedure comprising a cut slot corresponding to the calculated cut plane.
 2. The method of claim 1 wherein the global coordinate system of the plurality of 2D images of the patient's joint comprises a z-axis oriented approximately parallel to a longitudinal axis of the femur neck and an xy-plane oriented perpendicular to the z-axis and wherein the sequence of interior images of a neck of a femur is oriented perpendicular to the z-axis.
 3. The method of claim 1 further comprising: estimating a best fit linear segment for a shaft of the femur; and calculating an azimuthal angle and a polar angle for the orientation of a direction of the best fit linear segment corresponding to at least two of the center coordinates for the sequence of interior images of the neck of the femur relative to a direction of the best fit linear segment for a shaft of the femur.
 4. The method of claim 3 further comprising: estimating a length of the neck of the femur that extends from a first intersection of the neck of the femur with the shaft of the femur to a second intersection of the neck of the femur with a head of the femur.
 5. The method of claim 4 further comprising: estimating a length of a first minimum diameter for a first image of the sequence of interior images of the neck of the femur, the first image adjacent to the first intersection of the neck of the femur with the shaft of the femur; and identifying a first contact point and a second contact point within the first image of the sequence of interior images of the neck of the femur, the first contact point located at a first end of the first minimum diameter for the first image and the second contact point located at a second end of the first minimum diameter.
 6. The method of claim 5 further comprising: providing a first contact point region on a surface of the neck of the femur, the first contact point comprising the first contact point; and providing a second contact point region on a surface of the neck of the femur, the second contact point comprising the second contact point.
 7. The method of claim 6 further comprising identifying a fourth contact point within a second image of the sequence of interior images of the neck of the femur, the second image adjacent to the second intersection of the neck of the femur with the head of the femur.
 8. The method of claim 7 further comprising providing a third contact point region on a surface of the neck of the femur, the third contact point comprising the third contact point.
 9. The method of claim 8 wherein the cutting jig for the arthroplasty procedure further comprises a first contact extension configured to contact the neck of the femur at the first contact region, a second contact extension configured to contact the neck of the femur at the second contact region, and a third contact extension configured to contact the neck of the femur at the third contact region.
 10. The method of claim 1 wherein the cut slot corresponding to the calculated cut plane of the cutting jig for the arthroplasty procedure provides a guide for resection of a portion of a head of the femur and a portion of the neck of the femur.
 11. A system for processing a medical scan of a patient in preparation for an arthroplasty procedure on a human hip joint, the system comprising: a network interface configured to receive one or more medical images of a patient's anatomy; and a processing device in communication with the network interface; and a computer-readable medium in communication with the processing device configured to store information and instructions that, when executed by the processing device, performs the operations of: receiving a plurality of two-dimensional (2D) images of a patient's joint subject to the arthroplasty procedure at a computing device; providing a sequence of interior images of a neck of a femur from the plurality of 2D images of the patient's joint, the interior images corresponding to cross-section images of the neck of the femur and spaced apart by a positive distance; estimating a center coordinate for each of the sequence of interior images of the neck of the femur, the center coordinate corresponding to a coordinate in a global coordinate system of the plurality of 2D images of the patient's joint; calculating a best fit linear segment corresponding to at least two of the center coordinates for the sequence of interior images of the neck of the femur; calculating a cut plane for use during the arthroplasty procedure on a human hip, wherein the cut plane is perpendicular to the best fit linear segment corresponding to the at least two of the center coordinates for the sequence of interior images of the neck of the femur; and generating a cutting jig for the arthroplasty procedure comprising a cut slot corresponding to the calculated cut plane.
 12. The system of claim 11 wherein the global coordinate system of the plurality of 2D images of the patient's joint comprises a z-axis oriented approximately parallel to a longitudinal axis of the femur neck and an xy-plane oriented perpendicular to the z-axis and wherein the sequence of interior images of a neck of a femur is oriented perpendicular to the z-axis.
 13. The system of claim 11 wherein the instructions, when executed by the processing device, further performs the operations of: estimating a best fit linear segment for a shaft of the femur; and calculating an azimuthal angle and a polar angle for the orientation of a direction of the best fit linear segment corresponding to at least two of the center coordinates for the sequence of interior images of the neck of the femur relative to a direction of the best fit linear segment for a shaft of the femur.
 14. The system of claim 13 wherein the instructions, when executed by the processing device, further performs the operation of: estimating a length of the neck of the femur that extends from a first intersection of the neck of the femur with the shaft of the femur to a second intersection of the neck of the femur with a head of the femur.
 15. The system of claim 14 wherein the instructions, when executed by the processing device, further performs the operations of: estimating a length of a first minimum diameter for a first image of the sequence of interior images of the neck of the femur, the first image adjacent to the first intersection of the neck of the femur with the shaft of the femur; and identifying a first contact point and a second contact point within the first image of the sequence of interior images of the neck of the femur, the first contact point located at a first end of the first minimum diameter for the first image and the second contact point located at a second end of the first minimum diameter.
 16. The system of claim 15 wherein the instructions, when executed by the processing device, further performs the operations of: providing a first contact point region on a surface of the neck of the femur, the first contact point comprising the first contact point; and providing a second contact point region on a surface of the neck of the femur, the second contact point comprising the second contact point.
 17. The system of claim 16 wherein the instructions, when executed by the processing device, further performs the operation of: identifying a fourth contact point within a second image of the sequence of interior images of the neck of the femur, the second image adjacent to the second intersection of the neck of the femur with the head of the femur.
 18. The system of claim 17 wherein the instructions, when executed by the processing device, further performs the operation of: providing a third contact point region on a surface of the neck of the femur, the third contact point comprising the third contact point.
 19. The system of claim 18 wherein the cutting jig for the arthroplasty procedure further comprises a first contact extension configured to contact the neck of the femur at the first contact region, a second contact extension configured to contact the neck of the femur at the second contact region, and a third contact extension configured to contact the neck of the femur at the third contact region.
 20. The system of claim 11 wherein the cut slot corresponding to the calculated cut plane of the cutting jig for the arthroplasty procedure provides a guide for resection of a portion of a head of the femur and a portion of the neck of the femur. 